Rackets are described in terms of various specifications. Some specifications cannot be altered and are characteristic properties of the manufactured racket. These include, for example, frame stiffness and string bed density.
Frame stiffness is a measure of the resistance of the frame to bending upon impact. Stiffness is measured by a device that clamps the racket at the throat area, and physically bends the tip of the racket a standard deviation downward. See, for example, the device disclosed in U.S. Pat. No. 4,488,444). A higher measured value indicates greater frame stiffness.
String bed density is a function of the number of holes that enable strings to be placed through the side profile of the hitting area, and how close the string holes are placed together. The greater the number of holes and the closer the string holes are together, the greater the string bed density.
Other specifications that can be modified post racket production are overall weight, distribution of weight, balance point, and swing weight. The majority of rackets today are comprised of carbon fiber. Rackets found in stores and sold today are constructed to be superlight, and are made for the average tennis player. Rackets used by top competitive players are made heavier by the addition of lead tape at specific areas of the racket. The areas where additional weights are usually placed are on the string bed hoop (i.e., the oval shape) and inside the handle. Typically, additional weights are placed at locations along the hoop at the 12 o'clock position inside section of frame string bed area, the 3 o'clock position, and the 9 o'clock position. (See, for example, exemplary racket 100 shown in FIG. 1). The hoop areas of the frame are easily accessible and simple to modify by the addition of lead tape.
The addition of weight inside the handle of a racket is a difficult area to reach. Most weight added in this region is done by the manufacturer during construction of the frame. Even a small addition of weight, such as one gram, results in significant performance differences of the racket. These performance differences are so significant that top level professionals often spend up to two hundred U.S. dollars per frame to have their rackets and their custom measurements made exactly the same. This is necessary because there are always differences that exist from one machined racket to the next.
Furthermore, every racket has a balance point. There is one point on a frame that the racket will balance horizontally, or level like on a see-saw. Other than this finite point, the addition of weight to a racket will change the balance point. The addition of weight in the handle moves the balance point closer to the handle. The addition of weight on the head of the racket moves the balance point closer to the tip of the frame.
The swing weight of a racket is the sum of each atom's mass times the distance squared to the pivot point at 4.0 inches on the handle. The standard units of swing weight are kilograms times meters squared. Swing weight is measured by a machine that clamps the racket at 4.0 inches and circumferentially swings the racket on one level plane. (See again, for example, the machine disclosed in U.S. Pat. No. 4,488,444). The higher the swing weight value, the more weight the human hand perceives and the heavier the racket feels. The addition of weight at greater than 4.0 inches from the handle end of the racket increases swing weight. By definition, the addition of weight in the lower 4.0 inches of the racket handle has no effect on swing weight. The addition of weight in the handle, especially the terminal four inches, although inaccessible in current rackets, is of paramount importance in the playing characteristics of the racket.
What is needed in the art is a simple method of altering the weight of a racket along the entire length of the racket handle.